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#include <stdio.h>#include "mpi.h"#include <math.h>#include <stdlib.h>int main(int argc, char** argv) {	FILE *f;	int dim;	int res;	int nprocs, rank;	double* vector;	int width;	int nc;	int i, j;	int start, size;	int proc, p2;	double tmp;	double* result;	double* presult;	double data;	double time_start;	double time_end;		MPI_Status status;	/**	 * Init	 */	res = MPI_Init(&argc, &argv);	if (res != MPI_SUCCESS) {		printf("Error.\n");		MPI_Abort(MPI_COMM_WORLD, res);		return 2;	}	MPI_Comm_size(MPI_COMM_WORLD, &nprocs);	MPI_Comm_rank(MPI_COMM_WORLD, &rank);		if (nprocs < 2) {		if (rank == 0) {			printf("Requires at least 2 procs.\n");		}		MPI_Abort(MPI_COMM_WORLD, res);		return 1;	}	time_start = MPI_Wtime();	/*	 * Read data	 */	f = fopen(argv[1], "r");	fscanf(f, "%d", &dim);	if (rank == 0) {		printf("Matrix dimension: %d\n", dim);	}	vector = (double*)malloc(sizeof(double) * dim);	for (i=0; i<dim; i++) {		fscanf(f, "%lf", &vector[i]);	}	if (rank == 0) {		/*		 * Distribute		 */		nc = nprocs - 1;		width = (dim + nc/2 - 1) / nc;		start = 0;		if (width < 1) {			width = 1;		}		proc = 1;		size = width;		while (1) {			if (proc == nprocs-1) {				size = dim - start;			}			MPI_Send(&start, 1, MPI_INT, proc, 1, MPI_COMM_WORLD);			MPI_Send(&size, 1, MPI_INT, proc, 1, MPI_COMM_WORLD);			start += size;			proc++;			p2 = proc;			if (start >= dim) {				break;			}		}		start = -1;		while (proc < nprocs) {			MPI_Send(&start, 1, MPI_INT, proc, 1, MPI_COMM_WORLD);			proc++;		}	}	else {		MPI_Recv(&start, 1, MPI_INT, 0, 1, MPI_COMM_WORLD, &status);		if (start > -1) {			MPI_Recv(&size, 1, MPI_INT, 0, 1, MPI_COMM_WORLD, &status);			printf("[%d] start=%d, size=%d\n", rank, start, size);			/*			 * read data			 */			// skip first 'start' lines			for (i=0; i<start; i++) {				for (j=0; j<dim; j++) {					fscanf(f, "%lf", &tmp);				}			}			// read			result = (double*)malloc(sizeof(double) * (size));			for (i=0; i<size; i++) {				result[i] = 0;				for (j=0; j<dim; j++) {					fscanf(f, "%lf", &data);					result[i] += data * vector[j];				}			}			/*			 * send result			 */			MPI_Send(result, size, MPI_DOUBLE, 0, 1, MPI_COMM_WORLD);		}		else {			printf("[%d] skip\n", rank);		}	}	fflush(stdout);	MPI_Barrier(MPI_COMM_WORLD);	/*	 * retrieve result	 */	if (rank == 0) {		result = (double*)malloc(sizeof(double) * dim);		size = width;		start = 0;		presult = result;		for (i=1; i<p2; i++) {			if (i == p2-1) {				size = dim - start;			}			MPI_Recv(presult, size, MPI_DOUBLE, i, 1, MPI_COMM_WORLD, &status);			presult += size;			start += size;		}	}	time_end = MPI_Wtime();	/*	 * print result	 */	if (rank == 0) {		printf("Result:\n  ");		for (i=0; i<dim; i++) {			printf("%5.3f ", result[i]);		}		printf("\n");		printf("Execution time: %.4f\n", time_end - time_start);	}	MPI_Finalize();}